a. Field of the Invention
The present invention relates to an air filter unit using a filter bag and more particularly it relates to a method for preventing dust from being discharged into the atomosphere along with the clean filtered air after collected dust is shaken off and exhausted and before normal operation is effected.
B. Description of the Prior Art
Air filter units using filter bags are suitable for separation and collection of fine solid particles suspended in the air, such units being in general use. When such unit is industrially used in a factory for cleaning dust-rich exhaust gases, a large amount of dust is collected on the inner surface of the bag in a short time to the extent that continued operation would greatly decrease efficiency of collection. As a result, it is necessary to clean the filter bag at suitable intervals of time. Heretofore, the cleaning of the filter bag has been carried out by stopping the suction and exhaust operation and imparting vibrations to the filter bag to cause the collected dust to separate from the bag and fall down by gravity for exhaust. With such operation, however, dust, though small in amount, is discharged along with the clean filtered air during the initial stage of the next suction and exhaust operation (normal operation). This is because fine dust particles which have penetrated into the woven structure of the bag and between the fibers and hence lodged therein are driven out of the bag due to a shock and relaxation caused upon shaking. Since the amount of escape of dust is small, it was neglected and the escaping dust was not recovered in the past. But today when working enviroment and control of exhaust gases have become problems, it cannot be neglected. Therefore, even if such escaping dust is valueless, it is necessary to decrease the amount of escape of fine dust particles to zero particularly where they are harmful directly or indirectly to the human body. Particularly, since there is no suitable dust collector for smaller particle diameter other than this apparatus, it is necessary to prevent said dust from being discharged into the atmosphere while using this apparatus.